Apparatus for igniting miniature rockets



y 0, 1967 B. B. GOULD 3,322,067

. APPARATUS FOR IGNITING MINIATURE ROCKETS Original .Filed March 13, 1961 F'yzl INVENTOR. 5527' 5- 601MB United States Patent 3,322,067 APPARATUS FOR IGNITING MINIATURE ROCKETS BertB. Gould, Berkeley, Calif, assfgnor, by mesne assignments, to MB Associates, San Ramon, Calif. Continuation of application Ser. No. 95,391, Mar. 13, 1961. This application Feb. 4, 1965, Ser. No. 431,780 Claims. (Cl. 10270) This invention relates to a method and apparatus for igniting miniature solid propellant rockets.

This application is a continuation of my copending application Ser. No. 95,391, filed Mar. 1 3, 1961 (now abandoned), and entitled, Ignition Method.

The ignition of large solid propellant rockets is a well known art, but the ignition of miniature rockets involves serious problems. For one thing, the physical sizes are so small that conventional ignition systems cannot be scaled down sufliciently. Spotty or irregular ignition in a large propellant grain evens out in a very short period of time but in a miniature rocket this same period represents a major part or all of the burn time. Further, with large web thicknesses and large chambers, excess igniter heat will involve an increased mass of propellant but will have a small proportionate effect on the ignition pressures and burning characteristics. The miniature rockets to which this invention relates are extremely small in size wherein the rocket has a diameter of about one-tenth inch and a length of one and one-half inches. Ordinarily a central port of about 50 mils is employed with a nozzle throat diameter of 30 mils. It is obvious that ignition of such thin configurations of propellant is very sensitive to the mode of application and the amount of igniter heat. Uneven or excess heat can produce an ignition pressure wave that will be destructive to the rocket case; inadequate heat may result in excessive end or tail burning or in non-ignition.

It has been found by experiment that desirable ignition can be accomplished by a localized source of heat that effectively travels the length of the propellant grain. Said heat source is not sufficient to cause local ignition of the grain but initiates chemical reactions and gas evolution similar to those that normally occur in the layer immediately beneath a burning propellant surface. Said heat source is sufficient, however, to cause ignition after it has travelled substantially the length of the grain and has thereby effected sufficient gas evolution to increase the chamber pressure and fill the grain port with inflammable vapors.

A suitable fuse to accomplish ignition in such manner comprises a copper or aluminum wire of 2 to 6 mil diameter, coated with a pyrotechnic such as Sb S and Ba(NO a boron and KNO aluminum and K010 lead mononitroresorcinate and KClO aluminum and Fe O or aluminum and Fe O mixed with a small amount of binder of plastic or nitrocellulose.

In the drawings forming part of this application:

FIGURE 1 is a sectional view of a rocket motor casing with a fuse inserted preparatory to firing;

FIGURE 2 is a sectional view of the rocket motor of FIGURE 1 at the moment when propellant ignition is likely to occur; and

FIGURE 3 is an enlarged cross section of a typical coated ignition wire.

Turning now to a description of the drawings by reference characters, there is shown in FIGURE 1 a drawn metal casing 1 having a propellant grain 2 therein with a central port 3. The casing 1 is normally made of drawn metal and is adapted for insertion in an outer casing, not illustrated, having an aerodynamic nose thereon and guiding fins. Of course, in many instances, miniature rockets are made with only a single casing wherein the casing is drawn or otherwise formed to the desired external configuration and the propellant grain and nozzle placed directly therein. There is also shown in FIGURE 1 the nozzle 4, the internal portion of the fuse 5, and the external portion of the fuse 6. The internal fuse 5 is a pyrotechnic-coated wire, with a burn rate in the range of 1 to 10 inches per second, constructed as described herein. The external fuse 6 may be the same or a faster burning fuse whose purpose is to conduct flame from a triggering source 7 to the internal fuse 5. The structure of the internal fuse 5 is shown in FIGURE 3. The wire 9, which may be of a metal such as copper or aluminum is coated with a pyrotechnic 10 such as has been described above.

In FIGURE 2 there is shown the relationship of the components of the instant of ignition. The localized burning point 8 of the fuse has travelled through the port 3, heating the propellant surface and causing an evolution of inflammable vapor. The resistance to gas flow effected by the nozzle throat and the length of the grain port has increased the pressure at the point 8. As the remaining portion of the fuse 5 is consumed, ignition will occur throughout the surface of the grain port with substantial simultaneity and without a destructive pressure pulse.

I claim:

1. A miniature rocket engine embodying an ignition device comprising in combination a rocket engine having an elongate casing, a solid propellant grain within said casing, said solid propellant grain having a central burning port extending substantially the entire length thereof, and an ignition device comprising an elongate combustible support formed of a high heat conductive material and unconnected to the grain and having a cross-section which is a small fraction of the cross-section of the port and which extends substantially throughout the length of the burning port from the forward end to the rearward end thereof, and a pyrotechnic coating on at least that portion of the support which lies within the burning port to provide an ignition device having a burning rate of 1 to 10 inches per second, and means for ignition of the coated support adjacent the rearward end of the burning port, ignition of the propellant grain occurring when the pyrotechnic coated support has burned from the rearward end to the forward end portion of the central burning port.

2. A miniature rocket engine as claimed in claim 1 in which the support comprises a metal wire.

3. A miniature rocket engine as claimed in claim 2 in which the wire is formed of a metal selected from a group consisting of copper and aluminum.

4. A miniature rocket engine as claimed in claim 2 in which the metal wire is dimensioned to have a cross-section of 2 to 6 mils.

5. A miniature rocket engine as claimed in claim 1 in which the portion of the support extending beyond the burning port is coated with the pyrotechnic material.

6. A miniature rocket engine embodying an ignition device comprising in combination a rocket engine having an elongate casing, a solid propellant grain within said casing, said solid propellant grain having a central burning port extending substantially the entire length thereof, and an ignition device comprising an elongate combustible support unconnected to the grain and having a cross-section which is a small fraction of the cross-section of the port and which extends substantially throughout the length of the burning port and beyond the end thereof, and a pyrotechnic coating on at least that portion of the support which lies within the burning port, means for ignition of the coated support adjacent the rearward end of the burning port, and in which the portion of the support extending beyond the burning port is uncoated.

7. A miniature rocket engine incorporating an ignition device comprising in combination a rocket engine having an elongated casing, a solid propellant grain within said casing, said solid propellant grain having a central buming port therein extending substantially the entire length thereof, an ignition device comprising a combustible metal wire selected from the group consisting of copper and aluminum of from 2 to 6 mils diameter extending the length of the burning port and extending outwardly from said port, and a pyrotechnic coating on that portion of the wire which lies within the burning port said portion extending beyond the port being free of coating and means for igniting the uncoated wire extending beyond the port.

8. A miniature rocket engine as claimed in claim 7, wherein the pyrotechnic coating composition is selected from the group consisting of:

(A) Sb S and Ba(NO (B) boron and KNO (C) aluminum and KClO (D) lead mononitroresorcinate and K0103,

(E) aluminum and Fe O and (F) aluminum and Fe O 9. A miniature rocket engine as claimed in claim 8, wherein a binder of plastic is included in said composition.

10. A miniature rocket engine as claimed in claim 8, wherein a binder of nitrocellulose is included in said composition.

References Cited UNITED STATES PATENTS 1,567,267 12/1925 Hitt 10234.2 2,697,325 12/ 1954 Spaulding 10249 X 2,974,596 3/ 1961 Allen 102-70 3,044,399 7/1962 Easton 102---70 3,128,706 4/1964 Rumbel 6035.6

FOREIGN PATENTS 652,542 4/ 1951 Great Britain. 662,429 12/1951 Great Britain.

2 BENJAMIN A. BORCHELT, Primary Examiner.

G. H. GLANZMA'N, Assistant Examiner. 

1. A MINIATURE ROCKET ENGINE EMBODYING AN IGNITION DEVICE COMPRISING IN COMBINATION A ROCKET ENGINE HAVING AN ELONGATE CASING, A SOLID PROPELLANT GRAIN WITHIN SAID CASING, SAID SOLID PROPELLANT GRAIN HAVING A CENTRAL BURNING PORT EXTENDING SUBSTANTIALLY THE ENTIRE LENGTH THEREOF, AND AN IGNITION DEVICE COMPRISING AN ELONGATE COMBUSTIBLE SUPPORT FORMED OF A HIGH HEAT CONDUCTIVE MATERIAL AND UNCONNECTED TO THE GRAIN AND HAVING A CROSS-SECTION WHICH IS A SMALL FRACTION OF THE CROSS-SECTION OF THE PORT AND WHICH EXTENDS SUBSTANTIALLY THROUGHOUT THE LENGTH OF THE BURNING PORT FROM THE FORWARD END TO THE REARWARD END THEREOF, AND A PYROTECHNIC COATING AT LEAST THAT PORTION OF THE SUPPORT WHICH LIES WITHIN THE BURNING PORT TO PROVIDE AN IGNITION DEVICE HAVING A BURNING RATE OF 1 TO 10 INCHES PER SECOND, AND MEANS FOR IGNITION OF THE COATED SUPPORT ADJACENT THE REARWARD END OF THE BURNING PORT, IGNITION OF THE PROPELLANT GRAIN OCCURING WHEN THE PYROTECHNIC COATED SUPPORT HAS BURNED FROM THE REARWARD END TO THE FORWARD END PORTION OF THE CENTRAL BURNING PORT. 